756
FXUS02 KWBC 030701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE OCT 03 2023
VALID 12Z FRI OCT 06 2023 - 12Z TUE OCT 10 2023
...HEAVY RAIN AND FLASH FLOODING THREATS RAMP UP IN THE NORTHEAST
LATE WEEK...
..OVERVIEW
AN UPPER TROUGH AND LIKELY AN EMBEDDED UPPER LOW ARE FORECAST TO
SWING SLOWLY THROUGH THE GREAT LAKES REGION SOUTHWARD LATE THIS
WEEK INTO EARLY NEXT WEEK, WHILE A COLD FRONT SWEEPS THROUGH THE
EASTERN U.S. AT THE SURFACE. RAIN CHANCES WILL INCREASE ALONG AND
AHEAD OF THE FRONT, AND HEAVY RAINFALL MAY CAUSE FLOODING CONCERNS
IN THE NORTHEAST ON FRIDAY AND SATURDAY. SOME RAIN (WITH LAKE
EFFECT ENHANCEMENT) COULD LINGER INTO EARLY NEXT WEEK UNDERNEATH
THE UPPER LOW. MEANWHILE AN UPPER RIDGE SHOULD OVERTAKE THE
WESTERN U.S. FOR WARMER THAN AVERAGE TEMPERATURES AND GENERALLY
DRY CONDITIONS, UNTIL EARLY NEXT WEEK WHEN A TROUGH AND FRONTAL
SYSTEM COULD PUSH INTO THE PACIFIC NORTHWEST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN REASONABLY GOOD AGREEMENT WITH THE TROUGH
OVER THE GREAT LAKES, WITH THE PAST COUPLE MODEL CYCLES MORE
AGREEABLE IN FORMING A CLOSED LOW WITHIN THE TROUGH LIKELY OVER
THE WEEKEND. THE CLOSED LOW SERVES TO SLOW DOWN THE MOVEMENT OF
THE FEATURE, WITH ONLY A SLOW DRIFT IN ITS PLACEMENT EARLY NEXT
WEEK. DETERMINISTIC MODELS DO HAVE SOME SPREAD WITH ITS EVENTUAL
POSITIONING. GFS RUNS INCLUDING THE 18Z AND NEW 00Z RUN HAVING THE
UPPER LOW RETROGRADE TO THE SOUTHWEST DOES SEEM TO BE INCONSISTENT
WITH OTHER DETERMINISTIC AND ENSEMBLE GUIDANCE, SO THE GFS WAS NOT
PREFERRED AT THIS POINT.
BEHIND THE UPPER TROUGH/LOW, MODELS ALSO ARE AGREEABLE WITH AN
UPPER RIDGE SHIFTING FROM THE WEST COAST AT THE START OF THE
PERIOD FRIDAY GRADUALLY INTO THE INTERIOR WEST OVER THE
WEEKEND/EARLY NEXT WEEK AND THE CENTRAL U.S. BY TUESDAY. TROUGHING
COMING INTO THE EASTERN PACIFIC STEMMING FROM AN ALASKAN UPPER LOW
SHOWS SOME SPREAD IN ITS AXIS AND DEPTH BUT PRETTY MINOR FOR A
FEATURE IN THAT REGION FOR THAT LEAD TIME.
WITH THE REASONABLY GOOD CONSENSUS FOR THE LARGE SCALE PATTERN,
THE WPC FORECAST USED A BLEND OF THE DETERMINISTIC GUIDANCE
PARTICULARLY FAVORING THE 18Z GFS AND 12Z ECMWF EARLY IN THE
PERIOD, TRANSITIONING TO INCORPORATE THE ENSEMBLE MEANS TO HALF BY
DAY 6 AND JUST OVER HALF DAY 7 AS MODEL SPREAD INCREASED,
ESPECIALLY LESSENING THE GFS PROPORTION. CONTINUITY FROM THE
PREVIOUS FORECAST WAS GENERALLY WELL MAINTAINED.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER TROUGH AND FORMING EMBEDDED LOW TRACK ACROSS THE
GREAT LAKES LATE WEEK, ATLANTIC MOISTURE IS LIKELY TO FLOW INTO
THE NORTHEASTERN U.S., LEADING TO INCREASING RAIN TOTALS ON FRIDAY
AND ESPECIALLY BY SATURDAY ALONG AND AHEAD OF THE COLD FRONT.
INSTABILITY MAY BE SOMEWHAT LIMITED, BUT THE FORCING FOR ASCENT
WILL BE STRONG WITH THE RIGHT ENTRANCE REGION OF THE JET OVERHEAD,
AND PRECIPITABLE WATER ANOMALIES ARE FORECAST TO BE AT LEAST ABOVE
THE 75TH IF NOT THE 90TH PERCENTILE. RAIN AMOUNTS LOOK TO INCREASE
BY SATURDAY, WITH UPSLOPE FLOW/TERRAIN ENHANCEMENT LIKELY PLAYING
A ROLE IN THE INTERIOR NORTHEAST. THUS A MARGINAL RISK REMAINS IN
PLACE ACROSS THE LOWER GREAT LAKES REGION AND PARTS OF THE
NORTHERN MID-ATLANTIC AND NORTHEAST FOR DAY 4/FRIDAY, WITH A
SLIGHT RISK ACROSS THE INTERIOR NORTHEAST ON DAY 5/SATURDAY. MOST
HEAVY RAIN WILL EXIT BY SUNDAY BUT SOME LINGERING SHOWERS ARE
POSSIBLE UNDERNEATH THE UPPER LOW THROUGH EARLY NEXT WEEK, WITH
LAKE EFFECT RAIN SHOWERS LIKELY.
FARTHER SOUTH, THE TAIL END OF THE COLD FRONT COULD LINGER INTO
SOUTH TEXAS INTO AT LEAST FRIDAY, SPARKING ADDITIONAL SHOWERS AND
THUNDERSTORMS THERE AFTER A FEW WET DAYS. A MARGINAL RISK REMAINS
IN PLACE FOR THE DAY 4 ERO/FRIDAY. RAIN AMOUNTS LOOK TO GRADUALLY
LESSEN THIS WEEKEND INTO EARLY NEXT WEEK. MEANWHILE, CONDITIONS IN
THE WEST LOOK TO BE DRY UNDER THE UPPER RIDGE, ASIDE FROM LIMITED
SHOWERS POSSIBLE IN THE SOUTHWEST. THIS IS LIKELY TO CHANGE EARLY
NEXT WEEK AS A FRONT AND UPPER TROUGH APPROACH THE PACIFIC
NORTHWEST, CAUSING INCREASING PRECIPITATION CHANCES.
THE AMPLIFIED TROUGH AND THE COLD FRONT WILL LEAD TO COOLER
TEMPERATURES THAN AVERAGE, WHILE THE UPPER RIDGE TO THE WEST OF IT
SUPPORTS ABOVE NORMAL TEMPERATURES. ONE MORE WARMER THAN AVERAGE
DAY IS POSSIBLE IN THE NORTHEAST ON FRIDAY, WHILE HIGH
TEMPERATURES ACROSS THE PLAINS INTO MIDWEST WILL BE BELOW AVERAGE
BY 10-20F. LOWS LOOK TO BE A LITTLE LESS ANOMALOUS FRIDAY MORNING
BUT COULD DROP FURTHER ON SATURDAY, WITH LOW 30S AND PERHAPS A FEW
TEMPERATURES IN THE UPPER 20S IN THE NORTHERN HALF OF THE PLAINS,
CREATING THE POSSIBILITY OF THE FIRST FROST OR FREEZE OF THE
SEASON. AS THE UPPER TROUGH AND THE COLD FRONT(S) MARCH EAST INTO
THE WEEKEND, TEMPERATURES SHOULD COOL TO BELOW AVERAGE ACROSS THE
EAST-CENTRAL U.S. AND EVENTUALLY MAKING THEIR WAY TO THE EASTERN
SEABOARD BY EARLY NEXT WEEK. MEANWHILE THE ARRIVAL OF AN UPPER
RIDGE ACROSS THE WEST WILL FIRST RAISE TEMPERATURES ALONG THE WEST
COAST TO 10-15F ABOVE NORMAL, WITH SOME RECORD WARM LOWS POSSIBLE.
THE SHIFT/EXPANSION OF THE RIDGE FARTHER EAST SHOULD LEAD TO
WARMER THAN AVERAGE TEMPERATURES ACROSS THE NORTHERN ROCKIES INTO
THE HIGH PLAINS EARLY NEXT WEEK.
TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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